Many contaminated wastes and groundwaters contain organic pollutants which can be destroyed by hydroxyl radicals (*OH).
Hydroxyl radicals may be generated by a variety of reactions, including photolysis of hydrogen peroxide (J. H. Baxendale & J. A. Wilson, Trans. Farad. Soc. 52, 344, 1957), and Fenton's reaction, in which ferrous ion reacts with hydrogen peroxide to produce hydroxyl radical plus hydroxide ion (C. Walling, Acc. Chem. Res. 8, 125, 1976).
U.S. Pat. No. 5,043,080 discloses that when Fenton's reaction and photolysis of hydrogen peroxide are combined, there is a synergistic effect, giving a pollutant treatment process of enhanced efficiency. The wavelength of light and the ratio of metal ion to hydrogen peroxide were selected so that the major part of the UV light was absorbed by the hydrogen peroxide rather than the metal ions, while still allowing some absorption by the metal ions to regenerate the active form of the metal.
One of the drawbacks to this method is that in contaminated wastes of high inherent UV absorbance, light absorption by hydrogen peroxide, and therefore efficiency of treatment, can be seriously reduced.
There is also a limitation to the concentrations of contaminants that can be treated due to competitive absorption by byproducts.
Zepp et al. (Environ. Sci. Technol., (1992), vol. 26, p. 313) studied the generation of OH* resulting from the reaction of Fe (II) and H.sub.2 O.sub.2 and employed photolysis of Fe (III) complexes, including Fe (III) oxalate, as a convenient means of generating Fe (II) for their studies. On the basis of their results, these authors proposed that oxidation of organics may occur naturally in the environment by the H.sub.2 O.sub.2 /Fe (II) pathway. Their studies did not indicate that generation of Fe (II) by photolysis of Fe (III) oxalate would provide a practical process for degradation of organic contaminants.
Lunak et al. (Collection Czech. Chem. Commun. (1983), Vol. 48, p. 3033) examined the effect of potassium ferrioxalate on photolytic decomposition of H.sub.2 O.sub.2 as a means of determining the reaction mechanism of that photolysis. They observed that the ferrioxalate catalysed the decomposition of peroxide but they did not examine the potential of the process for oxidation of organics.
The processes described by these authors do not suggest that there is any advantage to be gained from employing the photolysis of ferric oxalate to generate Fe (II) for Fenton's reaction in the treatment of organic contaminants.